Slashdot videos: Now with more Slashdot!

View

Discuss

Share

We've improved Slashdot's video section; now you can view our video interviews, product close-ups and site visits with all the usual Slashdot options to comment, share, etc. No more walled garden! It's a work in progress -- we hope you'll check it out (Learn more about the recent updates).

MrSeb writes with news out of MIT about another interesting and potentially useful property of graphene. Researchers have known for several years that graphene generates electricity when exposed to sunlight, but incorrectly attributed it to the photovoltaic effect. A new paper shows that the current is actually generated from the much more unusual 'hot-carrier' response. Quoting:
"The material’s electrons, which carry current, are heated by the light, but the lattice of carbon nuclei that forms graphene’s backbone remains cool. It’s this difference in temperature within the material that produces the flow of electricity. ... Such differential heating has been observed before, but only under very special circumstances: either at ultralow temperatures (measured in thousandths of a degree above absolute zero), or when materials are blasted with intense energy from a high-power laser. This response in graphene, by contrast, occurs across a broad range of temperatures all the way up to room temperature, and with light no more intense than ordinary sunlight."
It will take more work to determine what new applications are reasonable from an efficiency perspective, but it does broaden graphene's already-impressive capabilities.

I was reading through a summary of the entire history of BitCoin on SomethingAwful and I lost any respect I ever had for that project and its participants. I made the right decision to not waste any electricity on it.

I was reading through a summary of the entire history of BitCoin on SomethingAwful and I lost any respect I ever had for that project and its participants. I made the right decision to not waste any electricity on it.

You are basing decisions about the validity and feasibility of BC based off of something posted on SA? Look, SA is a fucking hilarious site, but really? Do you get your investigative reporting from the Onion?

It depends what the replacement is. If the new "fuel" is direct sunlight, or wind, or thorium, etc., there is money to be made building and maintaining power plants, but no longer any real money to be made selling fuel -- because the primary cost is building the plant in the first place, not buying something to burn in it.

Producing in the labs vs producing in a manufacturing setting is worlds apart simply. Depending on the technology, there are lots of reasons why some takes decades to reach the market while others never reach it at all.

These include:1) economic viability (the technology costs too much)2) production viability (difficult if not impossible to produce at a large scale) which may require manufacturing technology to be developed as well or simply is impossible due to it's nature3) technological issues (which the

Additionally, a flood of breakthroughs leaves the investors with a multiplicity of choices and the question of which will win. You have to have a practical, economically viable, producible, reliable, safe product that will be a big enough step ahead of the competition that people will switch and which will STAY ahead of the competition long enough to pay off the investment plus a profit commesurate with the risk.

You also need to have the government out of the way. If it is "picking winners" (ala Solyndra)

Because science is occurring at such rapid speed that new innovations are always occurring and energy generation is a MAJOR issue currently in the world. A vast combination of graphene like this and solar/wind power could solve a great many problems. The current issue is that oil companies have a stranglehold on power generation as they are in alliance with the coal industry to keep us using non-renewable resources for the foreseeable future and it will take government intervention to stop that. Talk to

Talk to your right-wingers and libertarians about that before griping about science.

Where in my post did I gripe about science? My (rhetorical) question was intended to point out that there are many, many ways (indeed, which science has shown us) to deal with our energy issues, yet somehow we still can't get them past the laboratories. As you can see for the replies, there are many reasons why this is the case, very few of which have anything to do with science.

The largest problem I have had with coming around on the energy / global climate debate is that these horrible dire predictions are always accompanied by the most ineffectual proposals to mitigate the effects. No one is really coming out and saying straight up there is no solution we just must reduce consumption in a way that is incompatible with current society. Either they are wrong about the magnitude of the problem or wrong about how we should proceed to correct it. I was of the mind that they were w

In theory, all we need is a sufficiently high carbon tax or a cap and trade system with a very low cap. The free market would then decide the appropriate amount of decreased consumption vs. increased efficiency vs. cleaner sources vs. etc. That said, such a solution is not really politically possible when we can't even convince people global warming is real/caused by us/a problem. From a more practical standpoint, we need to throw every little solution we can at the problem, and doing those in steps is w

Because people like you never notice how much things actually *are* changing here in the real world.

Batteries are my favorite example. I'm constantly hearing people complain about reporting on battery breakthroughs in the lab, sarcastically saying, "Yeah, but when are we actually going to see these in the real world?" -- forgetting how much radically smaller and/or longer lived rechargeable batteries have gotten for increasingly high-power-consumption consumer electronics. Secondary cells have 5x'ed in energy density since the late 80s, and the trend shows no signs of slowing down. Even li-ion seems to have good life left in it (in particular, the anode; silicon (derided on Slashdot as a "sure, when will we finally see THAT?" tech) is now starting to replace carbon for part of the anode materials in commercially available cells, and it has a maximum theoretical anode energy density 10x that of carbon). Li-ion cathodes probably have a good 50% improvement left in them, possibly more; we'll probably see a migration to a Li-S chemistry after that, since that seems to be maturing the fastest (barring unexpected breakthroughs in Li-air, other chemistries, or electrostatic storage).

One nice thing about Li-S is that it's lower cell voltage with a much higher cell capacity, meaning that it's easier to get a specific desired voltage. Electrostatics would obviously be best (durability, temperature sensitivity, voltage discharge curve, etc), but they've also got the longest way to go. Li-air is oft hyped, but it too has an awfully long way to go. Then there's all sorts of other longer-shot contenders out there -- nickel-lithium, sodium-ion, aluminum secondary cells, etc. And then the question of whether flow batteries of any given chemistry will ever compete outside of a very narrow range of applications (such as grid storage).

Another area that's seen a lot of improvement is Low self-discharge NiMG batteries [wikipedia.org]. A few months ago i got around to replacing my old set of rechargeable batteries with a new set of these and i've been pretty impressed. They hold a bigger charge for longer, and they even seem to recharge faster, though that might just my optimistic thinking on my part. My only complaint is the charger requires me to recharge them in pairs rather than one battery at a time, but that's just an issue with the design of the cha

Its difficult to see the improvements in battery tech. Every improvement is met by electronic devices that consume more and more power meaning no real change in battery life in practice. More electrons might be flowing across these battery terminals, but the average Joe just sees the same amount of time they get to spend playing with their phone or whatever the device du jour is.

The article barely mentioned generating electricity from graphene and what was talked about the scientists was that they had no idea if it was possible. They did seem excited about using graphene as a new type of photo-detector.

Narrative I want to push? What the hell is that supposed to mean? Because I pose what I believe is a reasonable question about potential renewable energy sources never making it to market I'm pushing a narrative? I guess I should just STFU and not ask questions, eh?
The statement , “It is still unclear if it could be used for efficient energy generation. It’s too early to tell.” FTFA tells me it has potential for this purpose.

Almost all of them have some, fatal flaw, which may already be known or as yet unforeseen. In addition work often proceeds in small steps even if the jornalists make them sound big, the "next big thing" provides a 10/20% advantage (at best) in real world solutions, and takes time to reach its full potential so we just use it without noticing. In short by trying lots of thing at once we keep up steady progress, if we pick just one then we will stop.

Long story short... no. First, that isn't how science works. If I'm an expert in photovoltaic reactions, my help isn't very helpful while you're trying to get a windmill working. Scientist are, in general, specialists, there is no degree in "cool alternative energy technology". Second, that's not how markets work. If I'm really close to figuring out how to, say, increase solar cell efficiency by 50%, thus making me rich; I'm unlikely to give up that work because we're working on wind power this month. Finally, it would be foolish to put all of our eggs in one basket. It's unlikely that any currently feasible alternative energy systems will be able to supply all the power people need everywhere.

Deserts are great for solar, coastline are get for wind and hydro, volcanically active areas are great for geothermal... None of them is a perfect tech that will work everywhere. Seattle would find solar farms all but useless, and there's not much easily available geothermal in Detroit. There are a few "magic bullet" technologies being researched, but they are very theoretical and a risky "bet the farm" idea. Sure, controllable and safe fusion power would solve all our problems, but no one is entirely sure it's possible.

Well, this isn't a renewable energy source. It's just a funky property of Graphene. Far from generating any reasonable amount of energy this is just a low current induced by light. Could it lead to high efficiency solar power generation? Maybe, but that is extremely premature to think based on this story.

It sounds like they had to treat different sections of it to produce a gradient of some sort.

If the treatment is simple enough, then probably, yes.

I wish they would put out some actual numbers, like how much current and amperage they got off of how big a "panel" in sunlight, or a wavelength response study. They said that even IR made a response. That might well mean that you could harness HEAT. If that turned out to be the case, then this would be huge. As it is, it might be huge anyways.

This has absolutely nothing to do with light, and instead has absolutely incredible implications for power generation. Graphene geothermal probes for more efficiency, graphene cooling tubes for maximum gas/oil/coal electric power generation, nuclear power (bonus: extra radiation protection)... Hell, strap graphene to just about any process that involves waste heat and get power for "free!"

This has absolutely nothing to do with light, and instead has absolutely incredible implications for power generation. Graphene geothermal probes for more efficiency, graphene cooling tubes for maximum gas/oil/coal electric power generation, nuclear power (bonus: extra radiation protection)... Hell, strap graphene to just about any process that involves waste heat and get power for "free!"

This would be perfect in a car if they could use it to cool the engine as well as generate elecity without a generator.

This has absolutely nothing to do with light, and instead has absolutely incredible implications for power generation. Graphene geothermal probes for more efficiency, graphene cooling tubes for maximum gas/oil/coal electric power generation, nuclear power (bonus: extra radiation protection)... Hell, strap graphene to just about any process that involves waste heat and get power for "free!"

This would be perfect in a car if they could use it to cool the engine as well as generate elecity without a generator.

From TFA:

In most materials, superheated electrons would transfer energy to the lattice around them. In the case of graphene, however, that’s exceedingly hard to do, since the material’s strength means it takes very high energy to vibrate its lattice of carbon nuclei — so very little of the electrons’ heat is transferred to that lattice.

Perhaps I'm reading that wrong, but it sounds like it captures heat. Unless it rapidly converts said heat to electricity that strikes me as a good way to increase the heat in your engine compartment, not reduce it.

No, it captures heat by increasing electron mobility through the aromatic p-orbitals that pervade the entire sheet. That is, it converts heat into electron flow, ie electricity, without damaging the substrate.

increasing mobility or mobilizing electrons? It sounds like you are saying that it captures heat by exciting the potential of the p-orbital. This could cause electron flow across the Graphene sheet, but every electron that leaves the sheet would cause a charge imbalance and be a driving force to send that electron right back to the sheet.

Thus the need to set up a gradient of some sort to prevent back-flow (ie a diode), which was mentioned very generally in the article. I can't be any more specific than that, because I don't know the chemistry of the treatment or the physics of the interaction between the photon and the p-orbital.

The real problem is this: You can't beat Carnot. If you could, you could produce infinite energy.

Here's an example of why. Are you familiar with the term "COP" from the heating/cooling world? "Coefficient Of Performance". It's the ratio of how much energy you move against a thermal gradient versus how much energy you put in. Counterintuitively, perhaps, the numbers are often well greater than 1. Home AC systems, for example, are usually COP=2.5 to 4.0, and you may see commercial systems in the ~5.0 ba

Yes, Carnot's Law still applies to the sun. But on the upside, the theoretical maximum efficiency is very high, since the difference in temperature between the surface of the sun and the surface of the Earth is so great. In practice, there are a number of other limitations, however.

Since full spectrum light includes infrared, yes, it has a lot to do with light. Infrared heats the surface, causing electricity to be produced.Are there better sources of heat? oh certainly. However, without sunlight hitting the graphene, the discovery might have been delayed extensively.

Another accidental discovery (potentially) due to someone leaving their experiment out in the sunlight.

See my other post regarding combining this with a thorium thermal engine...

Billy Mays here! Are you disappointed at current materials? Want a super-strong wonder material that will let you build a space elevator while generating solar power at the same time? Well now there's Graphene! Yes, Graphene! See how much stronger and lighter it is than steel! Look at how it outperforms a traditional solar panel! The uses are practically limitless!

How much do you think a sheet of this stuff would cost per square foot? 100 million dollars? 70 million dollars? Well you

Perhaps this could be used on the receiving side of a "wireless" power system for spacecraft. A ship could have graphene panels pointed toward Earth where lasers, microwaves, or other forms of transmitted energy could provide power.

This is a very intriguing idea... The question I ask is, is it simply the temperature difference that causes the electricity flow, or does light actually have something to do with it? If it's just the temperature gradient, this could have great potential in places where there is no "sunlight" but there is heat.

Regular photovoltaics generate an electrical potential because charges liberated within the space-charge region of the P-N junction are caused to drift in opposite directions due to the built-in electric field that arises from the junction itself. I'm not seeing an equivalent mechanism here; if you can generate electrons by shining light on graphene, so what? You can generate electrons by shining light on a lot of things; in metals it's called the "photoelectric effect" and its been known for like a hundred

The summary is pretty bad, this is one where you need to RTFA. My initial reaction was pretty much the same as yours.

An excerpt (and sorry, I don't know how to do proper quotes):

"Instead, the MIT researchers found that shining light on a sheet of graphene, treated so that it had two regions with different electrical properties, creates a temperature difference that, in turn, generates a current. Graphene heats inconsistently when illuminated by a laser, Jarillo-Herrero and his colleagues found: The material

If it converts heat to electricity better than other materials that could make things interesting in harsher environments where solar panels aren't practical but extremes of temperature exist (like in desert regions). Match this with a water condenser and hellooooooo water vapor farming.

according to Bob Lazar, the aliens already have this. Alien spacecraft (currently on loan to the U.S. government) generate heat from an antimatter annihilation, and convert the heat directly into electricity using a near-100% efficient thermoelectric generator. No steam involved. Maybe graphene is!